1. Field of the Invention
This invention relates to a device for lifting crystal bodies, such as silicon single crystals, by the CZ method. It especially relates to the crystal-body clamping mechanism of a crystal-body-lifting device capable of safely lifting large-diameter crystal bodies, namely heavy crystal bodies. The crystal-body clamping mechanism clamps the neck portions formed on the top portion of crystal bodies during the lifting operation.
2. Description of Prior Art
In the process of lifting crystal bodies, such as silicon single crystals by the CZ method, a seed crystal installed within a seed-crystal holder suspended by a suspension member is guided to touch the free surface of the melted liquid of the raw material stored in a crucible. Then, the seed crystal is gradually lifted from the melted liquid and at the same time the suspension member is rotated to grow a single crystal beneath the lower portion of the seed crystal.
The number of chips with the same physical properties obtained from one piece of semiconductor wafer can be increases, as the diameter of the wafer increases. Therefore, for economic reasons, the need for large-diameter semiconductor wafers has been increasing in recent years. As the diameter of the crystal bodies enlarge, the weight of an individual single crystal increases. For example, the weight of a crystal body having 300 mm in diameter and 750 mm in body-length can reach a value more than 150 Kg.
In the process of lifting conventional lightweight crystal bodies, the load capacity of the small diameter portion beneath the seed crystal by using a dash neck method (hereinafter refer as dash neck) being lifted can afford to support the weight of the crystal body. Therefore, it is not necessary to make any reinforcement to its strength. However, in the event of supporting the above heavy crystal body by the strength of the dash neck alone, it is very difficult to maintain stable support of the whole weight of the crystal body if heat variation occurs in the surroundings of the crystal body, or an unexpected vibration, or a swinging of the crystal body is induced. As a result, when loads are concentrated at a so-called dash neck, which is a small-diameter portion for removing the dislocation from the seed crystal, the breakage of the dash neck and then the crystal body drops. This results not only the lost of crystal body but also a very great amount of damage of the lifting device.
To prevent the dropping of the crystal body, "a crystal lifting device" disclosed in Examined Japanese Patent Publication H7-10300 and "a device and a method for lifting single crystals" disclosed in Non-Examined Japanese Patent Publication H9-2893 are known. In both of the above lifting devices, a neck portion is formed on the top of the crystal body beforehand, and several holding levers or arms extending from the seed crystal holder clamp the neck portion.
However, for a crystal body of 300 mm diameter, the distance from the seed crystal holder to the neck portion is over 500 mm. Therefore, the above holding levers or arms should be longer than 500 mm. This will induce a very large moment to be imposed on the above holding levers or arms. It is also difficult to construct a mechanism having the strength enough to bear the moment within a confined space of the lifting device.
Furthermore, in the case of employing holding levers or arms, the crystal body can not be firmly grasped unless the neck portion is clamped rigidly by strong horizontal forces. Because stiff levers or arms are lacking in flexibility, a horizontal shifting of the crystal body would be incurred if the contact timing or the clamping forces of each the levers or arms are biased during the clamping of the crystal body. Therefore, there exists a danger that the crystal body will break at the neck portion.